An exposure apparatus comprises a stage apparatus which moves a wafer. Such a moving stage apparatus is disclosed in, e.g., Japanese Patent No. 3,145,355. In this stage apparatus, a Y slider which is guided by a yaw guide and a stage surface plate is mounted on the stage surface plate. Air pads are interposed between the Y slider, the stage surface plate, and the yaw guide.
An X slider is so arranged as to surround the Y slider. Air pads are interposed between the side surfaces of the Y and X sliders. Air pads are also arranged between the X slider and the stage surface plate. With this arrangement, the Y slider is slidable in the Y direction. The X slider is slidable in the X direction on the Y slider, and thus slidable in the X and Y directions.
The X and Y sliders are driven using linear motors. The linear motors for driving the X and Y sliders are of a coil-fixed, movable magnet type. A coil is selected in accordance with the magnet position, and the magnitude and direction of a current are properly controlled, realizing long-stroke driving.
This stage apparatus can perform high precision position control in a long stroke. When a six-axis fine moving stage capable of finely moving a substrate holding plate in X, Y, Z, θx, θy, and θz directions on the X slider is mounted on the X slider in the stage apparatus, a total mass of the X slider and a member on the X slider, i.e., a total mass of the X slider and fine moving stage increases. The exposure apparatus must accelerate the stage at high acceleration in order to increase the productivity. An increase in the total mass of the X slider and fine moving stage increases the force necessary for acceleration in proportion to the mass even at the same acceleration.
In the arrangement of the stage apparatus, a force for accelerating the X slider and fine moving stage in, e.g., the Y direction is generated by a Y linear motor. Part of the force is transferred to the X slider and fine moving stage via air pads. Letting m1 be the mass of the Y slider system, m2 be the mass of the X slider system, m3 be the mass of the fine moving stage system, and α be the acceleration, two Y linear motors generate a force (m1+m2+m3)×α. Of this force, a force (m2+m3)×α is transferred to the X slider and fine moving stage via air pads between the side surfaces of the Y and X sliders.
The force transfer ability of the air pad becomes a problem. Force transfer by the air pad is only about 1 kgf/cm2 in pressure conversion. If addition of the fine moving stage increases a force to be transferred to the X slider, the force may exceed the force transfer ability of the air pad. However, replacing the air pad with a rolling type guide is very difficult in an apparatus such as an exposure apparatus which is required to continuously operate for a long period and have high cleanliness because of shortening the useful life and generating dust.
Recently, demands have arisen for a stage apparatus suitable for use in a vacuum atmosphere in order to expose a fine pattern. To arrange air pads in the vacuum atmosphere, a means for recovering air must be arranged around the air pads. The periphery of this means does not contribute to thrust transfer, and the thrust transfer ability in pressure conversion further decreases.
In the arrangement of the stage apparatus, the noncontact guide between the X and Y sliders is formed by an air bearing such as a hydrostatic bearing, and constrained by spring rigidity. More specifically, the arrangement of a conventional stage apparatus is a coupled system in which one slider follows the motion of the other slider. This arrangement inhibits mechanical control (servo) of actively aligning the X and Y sliders, failing in high precision alignment.
When, for example, disturbance is added to the Y slider, an alignment servo system for the Y slider inevitably influences that for the X slider because of the coupled system in which the X and Y sliders are constrained by the spring rigidity. The X slider cannot be aligned at high precision.
Even if the Y slider is feedforward controlled in accordance with the position of the Y slider in order to cancel the moment of a force generated in the X slider, vibrations are added to the X slider. Both the X and Y sliders can hardly be aligned at high precision.
A conventional air bearing may be actively servoed. This method is poor in response characteristic, and hardly realizes high precision alignment. In this case, the system holds a gap between the X and Y sliders by a gap sensor. The response characteristic is poor in terms of the system arrangement, and it is difficult to achieve high precision alignment.